Rotary floor machines generally include a handle for operator control of the machine, a machine housing having wheels for mobility, and a pad mounted in the housing for circular rotation about a generally vertical axis. The machine is used in floor care and maintenance, with the pad used for buffing, burnishing, polishing, scrubbing, or other floor care operations. The pad is generally comprised of a loosely entwined synthetic material, such as polyester, and is subject to wear and replacement.
Machines of this type are generally supported by a pair of aft wheels to allow the machine to be easily displaced during operation and transported between jobs. In addition, there may also be a center caster disposed in a center aperture in the pad about which the pad rotates. The center caster maintains the machine housing above the floor, with the pad disposed in contact with the floor and immediately beneath the housing. Pad thickness varies widely among the various suppliers from 3/4 to 11/2 inches. Structural constraints and design limitations in the pad suspension and drive system have prevented current rotary floor care machines from accommodating this range of pad variation.
The triangular support arrangement of rotary floor care machines described above gives rise to another problem when pads of various thickness are employed. If the center caster is raised, the front of the pad is displaced upwardly and the rear of the pad downwardly causing uneven action between the pad and the floor. The tilted orientation of the pad results in a greater contact area with the floor toward the rear of the pad and a reduced contact area toward the front of the pad. The pad wears unevenly, reducing its useful life. This situation gives rise to another, more serious problem. For example, when the pad mounting and drive mechanism is raised to accommodate increased pad thickness, the inclined orientation of the pad securing mechanism results in reduced pad contact with the floor at the front of the machine even to the point where there may be no contact, while the rear of the pad is forced against the floor with increased pressure. This increased pressure may result in damage to the floor. Moreover, as the pad is rotated through a full revolution at the typically high operating speeds of such machines, i.e., on the order of 2000 RPM, the pad is highly compressed at the six o'clock position, i.e., nearest to the operator, and may not be compressed at all at the twelve o'clock position. At the two intermediate positions the pad material will be exposed to an intermediate pressure as it is compressed between the backing plate and the floor. As the pad is rotated at these high speeds and undergoes a large number of cycles of pinching and releasing, the pad tends to become free of the backing plate teeth which hold it in place. This is due to the non-woven structural nature of the pad itself and the manner in which it is secured to the backing plate of the pad assembly.
Referring to FIGS. 1 and 2, there is shown a partially cutaway side elevational view of a rotary floor machine 80 illustrating the nonuniform pad-floor engagement encountered in the prior art. The rotary floor machine 80 includes a pair of main support wheels 82 (only one of which is shown in the figure for simplicity) and a center caster 84. The center caster 84 is positioned within an aperture in the machine's rotary pad 88. Means are provided (although not shown in the figure for simplicity) to adjust the position of the caster 84 relative to the machine's housing 86. Thus, the housing 86 and pad 88 may be raised or lowered relative to the floor by adjusting the position of the caster 84 within the housing. The housing 86 pivots upward or downward about a pivot axis 90 aligned with the two main support wheels 82. Because the pad 88 is displaced about the pivot axis 90 and does not move in a true vertical direction as the height of the caster 84 is changed, a nonparallel alignment results between the pad and the floor. For example, when the caster 84 is extended from the housing 86 so as to raise the pad relative to the floor, the leading lower edge of the pad may be positioned above the floor as shown by the distance "X" in FIG. 1. Similarly, where the caster 84 is retracted into the housing 86 for the purpose of lowering the pad 88 relative to the floor, a gap "Y" may be formed between the aft, lower edge of the pad and the floor as shown in FIG. 2. In either case, uneven pad wear results and a poor burnishing is achieved because of the unevenness in applied pad pressure.
One attempt to solve the problem of irregular pad wear and floor damage caused by the use of pads of varying thickness in a three-wheeled rotary floor care machine is disclosed in U.S. Pat. No. 4,365,377. In this approach, a caster disposed within a centrally-located aperture in the pad is increasingly urged away from the housing of the machine as the caster and housing progressively approach one another with increasing compression of the pad. As the pad mounting arrangement is caused to be moved downwardly compressing a portion of the pad, the compression means, such as a coiled spring, exerts progressively increasing force upon the pad suspension arrangement to increasingly urge it back upwardly to a position wherein the pad is not compressed. This approach also suffers from pad "tilt" from front to back inherent in a triangular support arrangement.
Another common source of misalignment out of the horizontal in this type of support arrangement is caused by wheels of different diameter. Commercially available wheels used in rotary floor care machines are not precisely dimensioned and may vary considerably in diameter. This too gives rise to pad carrier misalignment and irregular and excessive pad wear.